Drop on demand piezo ink jet printing apparatus have been used to apply inks to a variety of substrates for a period of time. Generally, a drop on demand piezo ink jet printing apparatus operates to discharge individual droplets of ink onto a substrate in a predetermined pattern to be printed. Such an apparatus typically incorporates an array of orifices in a nozzle block, a plurality of control printheads, and a controller. The orifices are customarily arranged in a vertical row, and conventional ink jet printing apparatus have incorporated a separate printhead communicating with each orifice. The printheads are controlled by the controller, which can be keyed by an operator to operate the printhead according to a programmed schedule to print one or a series of characters or symbols.
Each orifice is designed to emit a single droplet of ink during each firing of its associated printhead. The droplets, emitted according to the programmed sequence, are directed toward a substrate where the character or symbol is printed. The quality of print produced by a drop on demand ink jet printer requires among other things, precise control over the size of the ink dot that impacts the substrate. Dot size in turn is affected by the size of an ink droplet discharged from a nozzle.
In the past, it was important in the overall design represented by the relationship between printhead characteristics, orifice size, and ink characteristics, that the droplets not only be of proper size but also that the size be consistent because otherwise the printed characters or symbols would be irregular in width. Of course the substrate or material may also affect the resulting image.
Admittedly, there has been much progress in the area of piezo jet printing however, heretofore, the piezo jet printers were limited in that they were not able to handle high-speed process printing. The inability of prior devices to perform the high-speed printing was due in part to the inability of the inks being processed to dry fast enough. That is, previously, the inks used were not adequately drying and therefore were not achieving or maintaining the registration necessary. Thus, prior attempts to process printing at high-speeds resulted in or caused a degradation of image quality, if any image was obtainable.
Furthermore, until recently, piezo jet printheads capable of processing inks and other compositions at high frequencies were not available. The evolution of printhead design has resulted in an ink jet device which is capable of high-frequency operation in accordance with the present invention. However, the mere ability to operate at high frequencies does not provide for processing of all inks and compositions, and has not heretofore provided the ability to maintain the registration of the printings, especially where the printer is operated at high frequency while the material is passed thereunder at high speeds. For it is one thing to operate at a high frequency or at high speed and quite another to operate at high frequency and high speed.
Thus there is a need for a process in which recently developed printheads may be used to provide high-speed process printing of materials.
While many improvements to conventional ink jet printing apparatus have been made, the piezo jet printing apparatus currently available lack the ability to create multi-color process images at high speeds, let alone in a single pass of the apparatus across the substrate (or a single pass of the substrate past the apparatus). There also remains a need for a substrate upon which high-speed process printing occurs yet the material is able to achieve a level of crockfastness higher than previously achieved under those printing conditions.